Load py_library and py_binary rules from @rules_python

This is to prepare for the Bazel incompatible flag
'load_python_rules_from_bzl'
(bazelbuild/bazel#9006).

Change-Id: If824c080a2c5b1e02a2eaeb6873aafd7afaf949f
GitOrigin-RevId: 767e391778adc345df482cccadc1875fab80021b

bazel/rules_flake8/BUILD.bazel

@@ -1,3 +1,4 @@
+load("@rules_python//python:defs.bzl", "py_binary")
 load("@flake8_deps//:requirements.bzl", "requirement")
 
 exports_files(

bazel/rules_protodoc/BUILD.bazel

@@ -1,3 +1,5 @@
+load("@rules_python//python:defs.bzl", "py_binary")
+
 py_binary(
     name = "protodoc",
     srcs = ["protodoc.py"],

bazel/rules_sphinx/def.bzl

@@ -1,3 +1,4 @@
+load("@rules_python//python:defs.bzl", "py_binary")
 load("@docs_deps//:requirements.bzl", "requirement")
 
 # Borrowed from Rules Go, licensed under Apache 2.
@@ -118,7 +119,7 @@ _sphinx_docs = rule(
 
 def sphinx_docs(name, extensions, **kwargs):
     sphinx_main_name = name + "_sphinx_main"
-    native.py_binary(
+    py_binary(
         name = sphinx_main_name,
         srcs = ["//bazel/rules_sphinx:sphinx_main.py"],
         visibility = ["//visibility:public"],

docs/sphinx_extensions/BUILD.bazel

@@ -1,3 +1,5 @@
+load("@rules_python//python:defs.bzl", "py_library")
+
 py_library(
     name = "sphinx_extensions",
     srcs = glob(["**/*.py"]),

examples/python/docs/BUILD.bazel

@@ -1,3 +1,4 @@
+load("@rules_python//python:defs.bzl", "py_binary")
 load("@grpc_python_dependencies//:requirements.bzl", "requirement")
 
 filegroup(

examples/python/hello_exchange/BUILD.bazel

@@ -1,3 +1,4 @@
+load("@rules_python//python:defs.bzl", "py_binary")
 load("@grpc_python_dependencies//:requirements.bzl", "requirement")
 
 filegroup(

python/BUILD.bazel

@@ -1,3 +1,5 @@
+load("@rules_python//python:defs.bzl", "py_library")
+
 exports_files(
     ["requirements.txt"],
     visibility = ["//visibility:public"],